IRC

It's a powerful chatroom server which allows you to basically...chat. You can make your own channels, PM (private message) people, register your nick/channel, have a vhost (virtual host), send people memos/messages (when they're offline), etc.

Server-wise: IRC Operators (Oper for short) can gline (network ban), kline (server ban), kill (disconnect a user forcefully from the network), and much more. IRC Operators are generally there to keep the server secure, and prevent spammers, botnets, attackers, etc. from doing damage/whatever to the network. And more.

Channel-wise: Channels owners can give people operator status, administrator status, half-operator status, voice status. Half-operators and above can make a channel a silent channel (only voiced users and above can talk, other users are prevented from sending messages). Half-operators and above can also ban and kick users from the channel. And more.

User-wise: Users can join many channels at once, as well as PM other people, and create scripts. Users can also register their nickname via NickServ, or channels via ChanServ. vHosts (Virtual Hosts), can also be used to mask your hostname, or to be used simply for fun.

There's many things I haven't mentioned here...but those are the basics. I can host a server for this forum/site if you want, it's all up to you.